The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head is generally an inductive write element that includes an electrically conductive coil that generates a magnetic flux in a write pole. The read head includes a magnetoresistive sensor. In current read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer.
Patterned magnetic recording media have been proposed to increase the bit density in magnetic recording data storage, such as hard disk drives. Patterned media can also be used for magnetic tape and other recording media such as compact disks. In magnetic patterned media, the magnetic material is patterned into small magnetically isolated blocks or islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional continuous media wherein a single “bit” may have multiple magnetic domains separated by domain walls. U.S. Pat. No. 5,820,769 is representative of various types of patterned media and their methods of fabrication. A description of magnetic recording systems with patterned media and their associated challenges is presented by R. L. White et al., “Patterned Media: A Viable Route to 50 Gbit/in2 and Up for Magnetic Recording”, IEEE Transactions on Magnetics, Vol. 33, No. 1, January 1997, 990-995.
In perpendicular patterned media applications, typically a magnetization in the up direction is considered North (N) and magnetization in the down direction is considered South (S). For longitudinal patterned media, magnetization in the left direction would be considered West (W) and magnetization in the right direction would be considered East (E).
Servo field are also typically used in hard disk drives to help the head stay aligned and to find the proper track. The servo field typically includes a sync field, an STM field, a cylinder ID field and a burst pattern. A sync field is generally used to synchronize data frequency. The STM field, otherwise called the servo start mark, is general used to mark the beginning of the servo information. The cylinder ID field is used to number the tracks and can also include the sector ID number. The burst pattern is used to properly position a head over a track.